Condensation polymers classification

In the last section we examined some of the categories into which polymers can be classified. Various aspects of molecular structure were used as the basis for classification in that section. Next we shall consider the chemical reactions that produce the molecules as a basis for classification. The objective of this discussion is simply to provide some orientation and to introduce some typical polymers. For this purpose a number of polymers may be classified as either addition or condensation polymers. Each of these classes of polymers are discussed in detail in Part II of this book, specifically Chaps. 5 and 6 for condensation and addition, respectively. Even though these categories are based on the reactions which produce the polymers, it should not be inferred that only two types of polymerization reactions exist. We have to start somewhere, and these two important categories are the usual place to begin. 

Another classification system, first suggested by Carothers in 1929, is based on the nature of the chemical reactions employed in the polymerisation. Here the two major groups are the condensation and the addition polymers. Condensation polymers are those prepared from monomers where reaction is accompanied by the loss of a small molecule, usually of water, for example polyesters which are formed by the condensation shown in Reaction 1.1. 

The chemical and physical properties of the polymers obtained by these alternate methods are identical, except insofar as they are affected by differences in molecular weight. In order to avoid the confusion which would result if classification of the products were to be based on the method of synthesis actually employed in each case, it has been proposed that the substance be referred to as a condensation polymer in such instances, irrespective of whether a condensation or an addition polymerization process was used in its preparation. The cyclic compound is after all a condensation product of one or more bifunctional compounds, and in this sense the linear polymer obtained from the cyclic intermediate can be regarded as the polymeric derivative of the bifunctional monomer(s). Furthermore, each of the polymers listed in Table III may be degraded to bifunctional monomers differing in composition from the structural unit, although such degradation of polyethylene oxide and the polythioether may be difficult. Apart from the demands of any particular definition, it is clearly desirable to include all of these substances among the condensation... 

The classification of a condensation polymer Is historically based on the observation that during polymerization a small molecule, such as water, is condensed or removed as part of the reaction. There are a large number of polymers produced from condensation reactions and only a representative sample is presented in... 

Using Carothers original classification, one would classify the polyurethanes as addition polymers, since the polymer has the same elemental composition as the sum of the monomers. However, the polyurethanes are structurally much more similar to the condensation polymers than to the addition polymers. The urethane linkage (—NH—CO—O—) has much in common with the ester (—CO—O—) and amide (—NH—CO—) linkages. 

To avoid the obviously incorrect classification of polyurethanes as well as of some other polymers as addition polymers, polymers have also been classified from a consideration of the chemical structure of the groups present in the polymer chains. Condensation polymers have been defined as those polymers whose repeating units are joined together by functional... 

It should not be taken for granted that all polymers that are defined as condensation polymers by Carothers classification will also be so defined by a consideration of the polymer chain structure. Some condensation polymers do not contain functional groups such as ester or amide in the polymer chain. An example is the phenol-formaldehyde polymers produced by the reaction of phenol (or substituted phenols) with formaldehyde... 

The broadest classification for plastics is the old thermoplastic and thermosetting . Examples of the former group are polyethylene, polystyrene, and poly-(methyl methacrylate) examples of the latter are urea-formaldehyde condensation polymers, powder coatings based on polyesters, epoxy resins, and vulcanized synthetic elastomers. 

It will be clear from these examples that this classification is now somewhat arbitrary. Many authors still refer to addition and condensation polymers in their current, conventional sense, however, and it is therefore necessary for the informed reader to understand this usage. 

There are two fundamental polymerization mechanisms. Classically, they have been differentiated as addition polymerization and condensation polymerization. In the addition process, no by-product is evolved, as in the polymerization of vinyl chloride (see below) whereas in the condensation process, just as in various condensation reactions (e.g., esterification, etherification, amidation, etc.) of organic chemistry, a low-molecular-weight by-product (e.g., H2O, HCl, etc.) is evolved. Polymers formed by addition polymerization do so by the successive addition of unsaturated monomer units in a chain reaction promoted by the active center. Therefore, addition polymerization is called chain polymerization. Similarly, condensation polymerization is referred to as step polymerization since the polymers in this case are formed by stepwise, intermolecular condensation of reactive groups. (The terms condensation and step are commonly used synonymously, as we shall do in this book, and so are the terms addition and chain. However, as it will be shown later in this section, these terms cannot always be used synonymously. In fact, the condensation-addition classification is primarily applicable to the composition or structure of polymers, whereas the step-chain classification applies to the mechanism of polymerization reactions.)... 

This is one of the oldest and most important classification criteria originally proposed by Carothers [3] in 1929 and the one that splits polymers into two major types addition and condensation polymers. The basis for the distinction is better understood by illustration with two examples belonging each one to one category polystyrene as an addition polymer and a polyester as a condensation polymer. They are produced by the reactions shown in Scheme 1.1. 

Although sometimes the classifications of condensation and step-growth polymers are considered to be interchangeable, as well as those of addition and chain-growth polymers, one must be aware that the classification of a polymer only by structure or only by mechanism may lead to ambiguities. Odian [8] recommends to classify a polymer attending both, structure and mechanism, in order to avoid this problem. Tables 1.3 and 1.4 contain examples of common addition and condensation polymers, respectively. 

A rational classification of polymers has been discussed for several decades. The debate began when Carothers proposed a classification according to the polymer reactivity and considered mainly two types of polymers polymers prepared through condensation reactions (condensation polymers) and those prepared by addition reactions (addition polymers). Chapter 1 of this handbook also discusses this topic, and although there are some overlaps in the topics covered here and in Chapter 1, the two chapters can be considered complementary. 

As disciissed in Chapter 1, under a scheme proposed by Carothers, polymers are classified as addition or condensation polymers depending on the type of polymerization reaction involved in their synthesis. This classification scheme, however, does not permit a complete difierentiation between the two classes of polymers. A more complete but still oversimplified scheme that is still based on the dilTerent polymerization processes places polymers into three classes condensation, addition, and ring-opening polymers. This scheme reflects the stractures of the starting monomers. Probably the most general classification scheme is based on the polymerization mechanism involved in polymer synthesis. Under this scheme, polymerization processes are classified as step-reaction (condensation) or chain-reaction (addition) polymerization. In this chapter, we will discuss the different types of polymers based on the different polymerization mechanisms. 

Later, in 1953, P.J. Flory divided the polymers by their reaction mechanism into chain-reaction and step-reaction, rather than by comparing the polymer s constitutional unit and the monomer. The addition polymers are generally produced by a chain reaction mechanism, and the condensation polymers produced by a step-reaction mechanism. Currently it is customary, though not scientifically correct, to refer to addition or chain-reaction polymerization and to condensation or step-reaction polymerization. Some have suggested that the classification of polymers... 

Further classification of polymers in the groups of additional polymers and condensation polymers has been on monomer composition, because this provides an orderly approach, whereas classification based on polymer uses, such as plastics, elastomers, fibers, coatings, etc. would result in too much overlap. For example, polyamides are used not only as synthetic fibers but also as thermoplastics molding compounds and polypropylene, which is used as a thermoplastic molding compound has also found uses as a fiber-forming material. 

According to the original classification of Carothers, condensation polymers are formed from hi- or polyfunctional monomers by reactions which involve elimination of some smaller molecule. A condensation polymer, according to t his definition, is one in which the repeating unit lacks certain atoms which were present in the monomers(s) from which the polymer was formed. 

Natural polymers are broadly classified as polysaccharides, proteins, polynucleotide, and natural rubber. This classification is based on the type of monomer building blocks for the polymer and type of covalent bonds for formation of the polymer. Polysaccharides that are carbohydrate polymers are formed by condensation of monomeric units called monosaccharides, proteins or peptide polymers are formed from amino acids and polynucleotide are synthesized from nucleotide condensation reaction forming glycosidic, peptide, and phosphodiester bonds, respectively. All natural polymers are condensation polymers. 

Adipic acid/dimethylaminohydroxypropyl diethylenetriamine copolymer CAS 61840-27-5 13318401-7 Synonyms Hexanedioic acid, polymer with 1-(bis (2-aminoethyl) amino-3-(dimethylamino)-2-propanol Polyamide-polyamine-epichlorohydrin resin Classification Condensation polymer Uses Antistat, film-former in cosmetics, hair care lubricant, conditioner for shampoos, hair conditioners binder component in aq. inks wet str. additive in paper in paper/paperboard in contact with aq./fatty foods Features Substantive to hair Regulatory FDA 21CFR 176.170 Trade Name Synonyms Cartaretin F-4 [Clariant http //www.clariant.com, http //www.clariant-northamerica.com], Cartaretin F-23 [Clariant http //www. ciariant. com, http //www. ciariant-northamerica. com]... 

Industrialists and technologists often classify polymers as either thermoplastics or thermoset plastics rather than as addition or condensation polymers. This classification takes into account their thermal properties. 

---